What causes the 'No transport provider' error in Outlook?

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Microsoft’s outlook will give a generic “No transport provider” error to a large number of problems. This FAQ entry summarises some of them.


  • GMS allows you to reject email immediately if the user account does not exist on the mail server. This reduces the number of errant messages and bandwidth consumed when mistakes are made. When >GMS tells Outlook that the user account does not exist, Outlook responds with a message like:
    Sent: M/DD/YYYY H:MM PM
    The following recipient(s) could not be reached:
    'user@domain' on M/DD/YYYY H:MM PM
    No transport provider was available for delivery
    to this recipient.

    and the message is not sent.

    To resolve the problem, either (a) get users to use the correct email addresses; or (b) change the “Unknown User Action” and manage the mis-directed email by hand.

  • Check your mail relay, if you are trying to send external mail check that the IP address you are sending from is listed in the Local IP listing. “No
    transport provider available” is Outlook’s way of saying “500 – Mail Relay
    not allowed at this server”

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